JPH027233Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion chamber of a diesel engine, and more particularly to a combustion chamber of a diesel engine with a cavity that improves the air utilization rate of injected fuel.

Fuel is injected into the combustion chamber of a diesel engine every time the piston reaches near compression top dead center. The injected fuel is dispersed in the air within the combustion chamber, chemically combines with oxygen in the air, and burns. The heat energy obtained from this is then used by a diesel engine.
It is converted into mechanical rotational force and output. In such a diesel engine, it is necessary to completely burn the injected fuel in the combustion chamber as much as possible in order to improve the output, and efforts are being made to improve the fuel combustion conditions.

By the way, in direct injection, a cavity is formed at the top of the piston, a swirl is generated in this cavity during the intake stroke, and fuel is directly injected during the swirl to promote mixing of fuel with air and improve air utilization efficiency. In this type of diesel engine, the quality of its combustion characteristics varies depending on the shape of the cavity that forms the main part of the combustion chamber.

For example, as disclosed in Japanese Unexamined Patent Publication No. 55-75530, recesses are sometimes formed uniformly in the inner circumferential direction of the cavity for the purpose of suppressing the amount of NOx produced. Furthermore, as shown in FIGS. 1 and 2, in a direct injection diesel engine that injects fuel using an injection nozzle 2 having four injection holes in a combustion chamber 1, the spray bundle G from each injection hole is transferred to the cavity. It is injected in four directions, which are the directions of the inner peripheral wall 3. In this case, each spray bundle G
is also affected by the swirl S, is evenly distributed inside the cavity, and burns. but,
As shown in FIG. 2, most of the spray bundle G that has advanced toward the inner circumferential wall 3 of the cavity is diffused toward the bottom wall 4 and collected at the center of the cavity. For this reason, the proportion of air in the cavity central space area A that encounters fuel is small, creating an area with poor air utilization.

The object of the present invention is to provide a combustion chamber for a diesel engine that can increase air utilization.

The present invention consists of a continuous wall portion that extends uniformly and continuously in the depth direction of the cavity, and a discontinuous wall portion that curves to protrude toward the center of the cavity and then discontinuously extends toward the lower wall side. It is characterized in that it is formed by alternately arranging the wall portions in the inner circumferential direction.

The present invention will be described below with reference to the accompanying drawings.

FIG. 4 shows the cylinder block 10, piston 11, and cylinder head 12 of a diesel engine, and the piston 11 has reached near the compression top dead center. At this time, the piston and cylinder head 1
The combustion chamber 13 between the two pistons is mainly formed by the inside of a cavity recessed in the piston top 111 and a small gap between the piston top surface and the cylinder head 12. In such a combustion chamber 13, a cylinder head 1 is installed.
Fuel injection is performed by a fuel injection nozzle 14 supported by 2. In this case, the direction of the injection hole of the nozzle is determined so that the fine fuel powder is diffused inside the cavity where there is a lot of air. This fuel injection nozzle has six injection holes, and injects fuel at equal intervals in the direction of the annular inner circumferential wall 15 of the cavity, as shown in FIG. 3 in plan view. The central cavity of the piston top 111 is formed by a circular open end 16, an inner circumferential wall 15 extending from the open end in the depth direction D of the cavity, and a bottom wall 17 continuing to the lower end of the inner circumferential wall. As shown in FIG. 3, the inner circumferential wall 15 of the cavity is divided into six sections in the inner circumferential direction in plan view, and each section is formed by alternately arranging two different shaped wall sections. . One of these two differently shaped wall portions is formed into a uniform flat continuous wall portion 151 that continues in the depth direction D of the cavity,
The other is formed into a discontinuous wall portion 152 . This discontinuous wall section extends in the depth direction D up to the depth h1 in the same way as the continuous wall section 151 side, and from the subsequent depth h1 to h2, the wall surface protrudes toward the center of the cavity. The curved surface a and the space between the curved surface a and the bottom wall 17 are respectively formed as surfaces extending in a direction bent with respect to the extending direction of the curved surface a. Note that, as shown in FIG. 4, the six injection holes of the fuel injection nozzle 14 described above are located closer to each discontinuous wall portion 15 from the injection direction with respect to each continuous wall portion 151 in a side view.
2 is maintained upward, thereby causing the fuel spray bundle G directed toward the discontinuous wall portion 152 to collide above the curved surface a (in FIG. 4).

The combustion chamber 13 of such a diesel engine changes its volume as the piston 11 reciprocates within the cylinder block 10, and receives fuel injection when the piston reaches near compression top dead center. In this case, each spray bundle G from the six nozzle holes has a continuous wall portion 151 or a discontinuous wall portion 152.
Most of the fuel injected toward the continuous wall portion 151 descends on the wall surface and further diffuses along the bottom wall 17 to the center of the bottom wall. On the other hand, the discontinuous wall portion 15
After colliding with the wall, most of the fuel heading toward the bottom wall is prevented from descending toward the bottom wall by the curved surface a of the wall, and the flow direction is changed by the curved surface a, leaving the curved surface a and flowing into the cavity. Diffusion into central spatial area A. The fine fuel powder thus diffused inside the cavity is also affected by the swirl S, and is uniformly diffused into the air inside the cavity and combusted, thereby causing the diesel engine to generate its output.

In this way, according to the combustion chamber 13 of the diesel engine shown in FIGS. 3 and 4, among the spray bundles G, those that collide with the continuous wall portion 151 are diffused toward the bottom wall 17 side of the cavity, Objects that collide with the discontinuous wall portion 152 can be separated from the wall side by the curved surface a and diffused into the central space area A of the cavity, and the air inside the cavity can be used equally both two-dimensionally and three-dimensionally. , it is possible to measure an improvement in air utilization efficiency, and in turn, it is possible to measure an increase in output.

In the above, a fuel injection nozzle 14 having six injection holes was attached to the combustion chamber 13, and the six spray bundles G were injected toward the inner circumferential wall 15 of the cavity divided into six parts. However, instead of this, as shown in FIGS. 5 and 6, the eight spray bundles G may be injected toward the inner circumferential wall 19 divided into eight parts by the injection nozzle 18 having eight injection holes. . In this case, the opening edge of the cavity is formed into a substantially square shape (in plan view), and the inner circumferential wall 19 is alternately continuous walls 191 and discontinuous walls 191 in the inner circumferential direction.
It is formed by arranging 92. Here again, the continuous wall 191 has a uniformly flat wall surface in the depth direction D, and the discontinuous wall 192 is formed as a wall surface with a curved surface a at the middle portion in the depth direction D.
Further, as shown in FIGS. 7 and 8, the opening edge of the cavity is formed into a circle (in plan view), and the inner peripheral wall 20 is divided into a continuous wall 201 and a discontinuous wall 202.
It may also be formed by alternately arranging them in the circumferential direction.

Even if the cavities of the pistons shown in FIGS. 5 to 8 are used, the air utilization rate inside the cavities can be increased in the same way as the combustion chamber 13 shown in FIGS. 3 and 4. In particular, the greater the number of spray bundles G and the greater the number of continuous and discontinuous sections of the inner circumferential wall, the more uniform the fuel dispersion becomes, and the more the air utilization rate can be increased.

[Brief explanation of drawings]

Fig. 1 is a plan view of a conventional piston, Fig. 2 is a sectional view of a main part of a diesel engine equipped with the piston shown in Fig. 1, and Figs. 3, 5, and 7 are different embodiments of the present invention. Fig. 4 is a plan view of each piston forming the combustion chamber of a diesel engine.
6 is a sectional view taken along the line X--X in FIG. 5, and FIG. 8 is a sectional view taken along the Y--Y line in FIG. 7. 11... Piston, 111... Piston top,
12... Cylinder head, 13... Combustion chamber of diesel engine, 16... Open end, 17... Bottom wall, 1
5, 19, 20... Inner peripheral wall, 151, 191, 2
01... Continuous wall part, 152, 192, 202...
Discontinuous wall portion, D...depth direction.

Claims (1)

[Scope of utility model registration request] A cavity is formed between the top of the piston and the cylinder head, and when the piston reaches near compression top dead center, fuel is injected directly toward the inner peripheral wall between the open end of the cavity and the bottom wall. In the combustion chamber of a diesel engine, the inner circumferential wall of the cavity has a continuous wall portion that extends uniformly and continuously in the depth direction of the cavity, and a continuous wall portion that protrudes toward the center of the cavity and then discontinuously extends. A combustion chamber for a diesel engine, characterized in that it is formed by alternately arranging discontinuous wall portions extending toward the bottom wall in the inner circumferential direction.